Appliance Control: Making Things Do Stuff - Smart Home Automation with Linux and Raspberry Pi - page 47

IR-RF-IR Gateways
These devices relay IR data through the air, at the 433MHz radio frequency used by so much wireless equipment,
before being replayed. For these devices, you have a choice between IR-only transmissions and TV senders.
An IR-only transmitter, such as the Powermid XL, is the simplest of these devices and will allow you to remotely
control devices without installing cables or sockets. They are fairly cheap but pass only IR data, so the controlled
device must be able to have an impact on you when you're in another room.
TV senders are the wireless versions of the over-the-aerial cables or old TV distribution systems, which involved
an aerial amplifier and a separate aerial cable into each TV in the house. The TV sender takes a single input and
transmits it to whichever receivers are listening, encoding whatever IR signals it also saw. There are many variants on
the market, including those with SCART sockets (instead of the old-school coaxial aerial sockets) and RCA composite
video. Even the cheaper models often have a “channel” switch on them, allowing multiple receiver-transmitter pairs to
be used in the same house without the signals getting mixed up. And with these devices becoming more mainstream,
some are almost as cheap as an IR-only transmitter, with the TV functionality becoming a free bonus feature.
IR Over IP
It is also possible to send data over your existing Ethernet cables, using devices such as the Keene IR Anywhere over
IP (KIRA). This eliminates any distance or interference issues you might get from the other methods and also provides
a way of remotely controlling IR devices from a computer, without needing to have the computer and its IR transmitter
physically in range of the device.
Being IP-controlled also means that IR signals can be sent via the Internet. Although this is pointless in itself
(because you can't derive any benefit from changing the TV channel when you're not sitting watching it), it does
provide an off-the-shelf way of controlling IR-based devices from a remote computer. And if something can be
controlled from a computer, then it can be controlled from anything connected to the computer, such as a web page
or cron job.
Using KIRA to retransmit IR codes first requires that you teach it those codes in the first place. This is done by
generating text files, using the software shown in Figure 1-15 .